A bumper car is usually driven by a crazed carnival-goer -- but we're going to build a self-driving Bumper Bot! This bot will use the Circuit Playground Express for brains and collision detection with its onboard accelerometer. The Crickit will provide all the muscle needed to drive two TT DC gearbox motors, as well as a micro servo direction indicator flag.

A small speaker and NeoPixels will also give us feedback while to bumper bot is out there having fun!!

Parts

Materials and Tools

• Small and medium corrugated cardboard boxes
• Ruler
• Hobby knife or scissors
• Paper clip or safety pin
• Double stick foam tape

You can watch the John Park's Workshop livestream build of the Bumper Bot here:

Cut the Cardboard Chassis

Attach Motors

Add Battery Pack

Connect Wheels

Affix Crickit

Plug In Power

Plug the battery connector into the Crickit power jack.

Connect Motor Wiring

Paper Clip Tail Dragger

A tail dragging bot needs something to smoothly glide across the ground while providing stability for the cart. Sometimes a ball caster is used for this, but we can get away with something much simpler here -- a paper clip! Our bumper bot is light enough that the humble paper clip will provide the needed stability and smoothness on the surface.

Add Speaker

Connect Servo

Mount the Bumper

This step is optional, but you may find it helpful. You can add a cardboard bumper to the front of the bumper bot so that it won't accidentally drive over lower obstacles that are cleared by the chassis.

Next, it's time to code the Bumper Bot with MakeCode.

You can code your Crickit and Circuit Playground Express using MakeCode! If you aren't already familiar with MakeCode, check out this guide to get started, then return here when you're ready.

Crickit Extension

The good folks at Microsoft's MakeCode team have been busily adding Crickit functionality to MakeCode! Currently, this works with the beta version of MakeCode, so click this link to get started. Then, create a new project.

To enable Crickit functionality in MakeCode, click on the Advanced category, then click on Extensions.

Then, type 'crickit' in the text field and press enter. The Crickit package will appear. Click on it and it'll be added to MakeCode!

Now that the package has been added, you'll see a new block category appear named Crickit

Click on the Crickit category to see all of the things you'll be able to do.

Crickit Run Motor

We'll start with the fundamental block for our program -- crickit run motor

Add one of these blocks to the Forever block. This will cause Motor 1 to run at half speed, forever!

Name and download the program, saving the .uf2 file to a directory you can easily find.

Then, plug the Circuit Playground Express (CPX) into you computer over USB (make sure to plug into the CPX USB port, not the one on the Crickit, which is used for occasional firmware updates) click the reset button on the CPX once to enter bootloader mode. Copy the .uf2 file to the CPX by dragging it to the CPLAYBOOT drive that appears.

Make sure the battery pack is plugged into the Crickit, and that the Crickit's power switch is in the 'on' position.

When the Circuit Playground Express restarts, it will tell the Crickit to run the motor. It's alive!! This will cause your Bumper Bot to turn in a circle. Turn off the Crickit board, and now we'll put the full program on it!

Bumper Bot Program Flow

Here's the flow we'll follow for our program:

• Turn on the bot, it will:
  • play a sound
  • set the NeoPixels to yellow
  • move the servo flag up
• Press button A on the CPX and it'll:
  • play a tone
  • set the NeoPixels blue
  • move the motors forward to start driving
  • flip the flag direction
• Press button B to:
  • stop the motors
  • play a double beep
  • set pixels to magenta
  • move the flag
• When the bot hits an object, the accelerometer shake condition is met:
  • stop both motors
  • reverse the motor direction
  • play a double beep
  • set the pixels to purple
  • move the flag
  • run both motors backwards for a little bit
  • stop Motor 2
  • run Motor 1, which causes the bot to turn
  • run the motors forward
  • set the pixels blue
  • rotate the flag

Following these steps, we create the program below. You can download the code and copy it to your Circuit Playground Express.

If you'd like to make changes, it's easy! How about different colors for the pixles? Change the sounds! Rotate the opposite direction when turning! There are so many choices for what you can do with your Bumper Bot and MakeCode!

On the next page, we'll put the bot into action!

Now you can set your Bumper Bot free! First, set the bot down on a smooth surface, such as a workbench or floor. Then, turn on the Crickit's power switch. It will boot up, light the NeoPixel ring yellow, play a startup beep, and move the servo mounted flag. Press the A button, and off it goes!

When it hits a wall or other solid obstacle, the accelerometer will sense the shake and reverse the motors, then turn, and start going forward again.

If the bot hits a soft obstacle it may not be enough to trigger the accelerometer shake detection, so you will need to help your robot friend along a bit! You can see this in the above video.

Have fun running your robot! You can create obstacle courses with coffee cans filled with sand or rocks, or even build two bots and have them battle each other for space!